The present invention relates to a magnetic disc memory apparatus such as of a CSS (Contact Start/Stop) Type.
In recent years, the disc memory of a CSS system or type has occupied a major part of the magnetic disc memories destined for use as external storage equipment for computer systems. In this connection, with the term "CSS system", such a magnetic disc memory is meant in which a floating magnetic head slider is in contact with a disc surface when the magnetic disc is stationary, while the floating head slider is caused to float above the disc surface upon rotation of the latter. The magnetic disc memory of the CSS type is an improvement upon the magnetic disc memories heretofore in use in that a head loading mechanism of a complicated structure can be spared and that a loading force of the magnetic head (i.e. a force produced between the head and the disc) can be reduced to less than 1/10 as compared with that of the hereto known system, and thus enjoys advantages such as improved reliability, inexpensiveness and others. With the above-mentioned head loading system, the magnetic head is held at a position spaced from the disc surface when the disc is in the stationary state, and the magnetic head is pressed toward the disc surface under a predetermined pressure only after the disc has attained a steady rotating state, whereupon the magnetic head is brought to the balanced floating state under aerodynamic pressure produced at a slider portion of the magnetic head. Such a CSS type magnetic disc memory apparatus is disclosed, e.g., in U.S. patent application Ser. No. 337,032 filed Mar. 1, 1973, now U.S. Pat. No. 3,823,416, (Corresponding to Japanese Patent Application Laid-Open No. 121,514/74 laid open Nov. 20, 1974).
By the way, at present manufacturers are making every effort to increase the storage capacity of the magnetic disc memory. To this end, it is important to increase the number of tracks provided for each disc (increasing of the track density) and to increase the storage capacity of each track (increasing of the bit density). Above all, in order to increase the bit density, it is indispensable to hold stably the magnetic head gap at a position very close to the disc surface in consideration of magnetic recording characteristics as required. For this reason, roughness of the disc is reduced to thereby decrease a floating distance between the magnetic head and the disc surface. More particularly, referring to FIG. 1 of the accompanying drawings, a number of projections or protrusions 6 remain on the surface of the magnetic disc 8 without having been removed in the course of the manufacturing process and provide a major factor which determines the surface roughness of the disc. Reference numeral 1 denotes a floating type PG,4 magnetic head which is composed of a head slider 5 and a head core 10 provided with a winding 3. The magnetic head 1 is maintained in the floating state in which aerodynamic pressure produced by rotation (indicated by an arrow 9) of the disc 8 is balanced with a load given by the magnetic head 1 and represented by an arrow 2. Recording and reproduction of information are effected through a head gap 4 defined by the head core 10 and the head slider 5.
In connection with the magnetic disc memory apparatus of CSS type, it is however noted that adhesion takes place between the disc and the head slider, when the memory apparatus is left unused for a long time with the head remaining in contact with the head slider. In particular, when a lubricating oil is applied over the disc surface with a view to lengthening the useful life of the CSS disc system, as practiced commonly at present, the phenomenon of adhesion becomes more apparent. Moreover, if the memory system is left in an environment of high humidity, adhesion becomes more serious. Of course, adhesion by itself exerts substantially no adverse influence to the inherent function (i.e. recording and reproduction of information) of the memory system. However, when the disc is rotated starting from the state where the head is adhesively contacted to the disc surface, the head tends to be pulled in the circumferential direction of the disc due to the adhesion, resulting possibly in that gimbal and the like which support the head slider becomes injured or destroyed. Referring to FIG. 2 of the accompanying drawings, the head slider 5 is shown as supported by the gimbal 11 and applied with a load by a load arm 12 in the direction facing toward the disc surface. Assuming now that the head slider 5 is in adhesive contact with the disc surface 8 in the stationary state, rotation of the disc 8 starting from this state will cause the head slider 5 to be pulled and displaced in the circumferential direction of the disc 8, involving eventually deformation and possibly destruction of the gimbal 11 supporting the head slider 5, in case the adhesion is significant. On the other hand, in case the adhesion is less significant, the head slider will be precipitantly detached from the disc surface, having overcome the adhesion, at the instant when the head slider has been slightly displaced. Under the shock at that time, the disc surface will be bruised. In this manner, when the rotation of disc is started in the state where the head slider is adhesively contacted to the disc surface, the disc memory system will undergo damage and destruction in the worst case. To solve the difficulty encountered in the starting phase of operation of the magnetic disc memory of CSS type mentioned above, there have been heretofore adopted the following measures. First, the surface roughness of the disc surface is increased at the expense of the recording characteristics, to thereby prevent more or less occurrence of the adhesion; second, the quantity of lubricating oil applied over the disc surface is decreased; third, a desiccating agent is placed in the interior of the disc memory system to suppress increasing of humidity within the system, and so forth. However, these measures are ineffective for attaining a complete obviation of the adhesion phenomenon and do not provide fundamental remedy. Under the circumstances, the environmental conditions in which the CSS type memory system is used have to be necessarily regulated particularly in respect of humidity. And, false manipulation of the disc memory system by operator or user will lead directly to injury or destruction of the memory system, involving thus inconveniences in manipulation or handling of the disc memory.